Method of sealing electrical conductors into vitreous envelopes



.NOV. 29, 1938. H P- BARASCH 2,138,224

METHOD OF SEALING ELECTRICAL CONDUCTORS INTO VITREOUS ENVELOPES Filed Jan. ll, 1958 34am? 70M @msc/x4 Patented Nov. 29, 1938 UNITED STATES METHOD OF SEALING ELECTRICAL CON- DUCTORS INTO VITREOUSr ENVELOPES Hans Pius Barasch,

Kensington, London, Eng,-

land

Application January 11, 1938, Seal No. 184,484

In Great Britain January 12, 1937 4 Claims.

The present invention relates to methods of sealing electrical conductors into envelopes of quartz or other refractory vitreous materials, and is particularly applicable to the sealing of leading-in wires into the quartz envelopes of the so-called super-pressure mercury vapour luminous discharge tubes.

It has been proposed, in order to obtain a satisfactory seal, to employ as the leading-in wire for a discharge tube with a quartz envelope a very thin strip or ribbon of molybdenum. Ow-

ing to the extreme thinness of the ribbon, the amount of its expansion due to heating is too small to produce any fracture of the surrounding quartz. At the same time, in order to obtain a satisfactory seal, it has been hitherto necessary to employ an envelope which is so shaped that the portion of the envelope surrounding the leading-in molybdenum strip has a cross-section which more or less conforms to the cross-section of the strip. ,For example, it is customary to employ for this portion of the envelope a capillary tube having a substantially rectangular cross-section, the length of the rectangle being very large compared with the width. One object of the present invention is to avoid the necessity for any such specially shaped envelopes or parts thereof when employing a thin strip or ribbon of metal as the leading-in conductor. v Another object of the invention is to provid a highly efficient seal capable of withstanding the very high pressures and temperatures employed in super-pressure mercury vapour discharge tubes.

A further object of the invention is to provide a simple and efficient method of constructing such super-pressure mercury vapour discharge tubes.

According to the present invention a method of sealing an electrical conductor in the form of a very thin metallic ribbon into a refractory vitreous envelope comprises wrapping the conwhich t closely into the bore of the capillary tubes, each rod carrying at one end an electrode and at the other end an electrical conductor, the conductor and electrode being connected by a very thin metallic ribbon wound round the rod in the form of a helix, each rod being fused into a capillary tube so `that the two electrodes face one another in the envelope which is evacuated and lled with a suitable gas.

The invention will now be described by way of example with reference to the accompanying drawing in which Fig. l'is a perspective diagram showing the method of sealing according to the present invention;

Fig. 2 shows in part section a luminous discharge tube in which the leading-in wires are sealed by the method of the present invention; and

Fig. 3 shows in section an alternative form of electrode unit for use in a luminous discharge tube.

Referring to Fig, 1, the quartz envelope I of the vessel into which a leading-in Wire is to be sealed is formed with a constricted portion 2 of circular cross section and small bore. 'I'he leading-in wire 3 is in the form of a very thin ribbon of molybdenum having a thickness of the order of 15a which is wound helically round a quartz rod 4 having a cross-section which is very slightly smaller than the inner cross-section of the portion 2, so that the rod with the ribbon will just fit into the bore of the portion 2. The rod is pushed into the bore of the por-r tion 2 and the two are fused together along the whole of their length, thereby enclosing' the ribbon 3 to form a perfect seal.l

The application of the inventionto the manufacture of a superpressure mercury vapour luminous discharge tube will now be described with reference to Fig. 2.

The tube comprises a quartz envelope having two end portions in the form of capillary tubes 5.0i circular cross-section. A quartz rod 6 of circular cross section with an external diameter of very slightly less than internal diameter of the tubes 5 is provided with a short axial hole at each end, the diameter of the hole being 1 mm. At one end of the rod 6 a tungsten rod 1 of 1 mm. diameter is inserted into the hole and at the other end of the rod 6, one end of a tungsten wire 8 is inserted into the other hole. Around the rod 6 is tightly wrapped in the form of a helix a length of very thin molybdenum ribbon -9. One end of the ribbon is wrapped tightly round the tungsten rod 1 and is further slipped over the tungsten rod 1. The tungsten rod serves as an electrode, and the quartz sleeve acts as a shield to prevent the discharge from reaching the molybdenum ribbon. The other end of the molybdenum ribbon is secured to the tungsten wire 8. The complete unit consisting of the quartz rod and attached electrode member, molybdenum ribbon, and tungsten wire is inserted into the bore of a capillary tube 5, the electrode being nearest to the centre of the tube. An exactly similar unit Il is inserted into the bore of the other capillary tube from the other end, with its electrode facing the electrode of the rst mentioned unit. The wall of the capillary tube is then fused to the quartz rods along the whole length of the latter and also to the quartz sleeves, thus providing a long seal around'the molybdenum strip. The portion i 2 of the bore surrounding the tWo electrodes is then evacuated and filled with mercury vapour at the required pressure. The lengths of the quartz rods are so chosen that the total length of each seal is greater than the length of the discharge space.

If the discharge tube is to work on direct current one electrode is coated with a suitable electron emitting material, Whilst if the tube is to work on alternating current, both electrodes will be so coated.

An alternative form of electrode unit is shown in Fig. 3. A quartz rod I3 has a fine bore running along the whole of its length, the bore being provided with a constriction I4 near one end. A tungsten electrode i5 carrying a quartz sleeve i6 is pushed into one end of the bore until its tip reaches the constriction I4. A thin quartz rod il lls the remainder of the bore with the exception of an end portion into which is inserted the tungsten wire I8. The electrode l5 and wire I 8 are connected by the ribbon I9 the ends of which are wrapped round the electrode and wire respectively.

I claim as my invention:

1. In an electrical discharge device, an envelope and a seal for a leading-in conductor comprising a tube of refractory vitreous material forming a continuation of the envelope of said device, a rod of the same material as said tube inserted in the bore of said tube and fused thereto, and a thin metallic ribbon wrapped helically around said rod between said rod and said tube.

2. In an electric discharge device, an envelope and a seal for a leading-in conductor comprising a quartz tube forming a continuation of the envelope of said device, a quartz rod inserted in the bore of said quartz tube and fused thereto, and a thin molybdenum ribbon wrapped helically around said rod between said rod and said quartz tube.

3. A luminous electrical discharge tube comprising a quartz envelope, two end portions of said envelope in the form of quartz capilliary tubes, a pair of quartz rods fitting closely into the bore of said capillary tubes, each of said rods carrying at one end an electrode and at the other end an electrical conductor, said electrode and conductor being connected by a thin metallic ribbon wound round the rod in the form of a helix, each of said rods being fused into one of said capillary tubes so that said electrodes face one another in said envelope.

4. A luminous electrical discharge tube according to claim 3 wherein each of said electrodes carries a quartz sleeve between the operative end thereof and the junction of said electrode and said ribbon, each of said sleeves being fused in the bore of one of said capillary tubes.

HANS PIUS BARASCH. 

